The present invention relates to an apparatus for installing a heavy-weight upper structure, wherein a height of the heavy-weight upper structure loaded on a marine carrier is properly adjusted by a hydraulic height adjusting device to safely put the heavy-weight upper structure on a stationary lower structure installed to a seabed.
The process of putting down the heavy-weight upper structure combines with a process of introducing or draining sea water to or from a vessel to change a ballast of the vessel.
The conventional installation of the heavy-weight marine structure includes a method of lifting and lowering the heavy-weight upper structure by a marine crane and a method of putting down the heavy-weight upper structure by the ballast change of the marine carrier.
According to the method employing the marine crane, as the total weight of the upper structure is limited by lifting capability of the marine crane, the upper structure is separately manufactured, or a part of the upper structure is separately mounted thereon. In this instance, since the upper structure or equipment which is separately manufactured should be separately manufactured, transported, mounted and test-driven, an offshore installing period is extended, and the method is inefficient in view of economics, safety and efficiency.
Also, since the method employing the ballast change of the marine carrier depends on the ballast capacity of the carrier, it is not possible to quickly respond to the change of the marine environmental factors (e.g., wind speed and waves) during the process of installing the heavy-weight upper structure, and there is a limit to the reduction of the work time.
FIGS. 1 and 2 show an offshore structure installing apparatus having a member for adjusting a height of an upper structure by a hydraulic unit which is disclosed in Korean Patent Publication No. 10-0658882.
Referring to FIGS. 1 and 2, an upper structure 2 is disposed on a carrier 3, in which the carrier 3 transports the upper structure to an offshore installation location, with the upper structure 2 being supported by a height adjusting member 6 having hydraulic units 7a and 7b. 
The height adjusting unit 6 includes a lower bearing block 9a with a receiving hole for a guide portion 8 at a center thereof, the hydraulic units 7a and 7b each installed at both sides of the lower bearing block 9a to adjust the height of the upper structure 2, the guide portion 8 fitted into the receiving hole of the lower bearing block 9a, and an upper plate 9b installed on the guide portion 8 and having both ends connected to an upper portion of the respective hydraulic units 7a and 7b. 
The upper plate 9b is lifted by the hydraulic units 7a and 7b, and the guide portion 8 connected to the upper plate 9b is guided by the receiving hole of the lower bearing block 9a in a vertical direction to adjust the height, thereby adjusting the height of the upper structure 2 installed thereon. Therefore, the upper structure can be seated on the lower structure 1 fixed to a seabed.
In case of the offshore structure installing apparatus, however, since the horizontal load of the carrier 3 or the upper structure 2 which is generated by the wind speed or waves is supported by the guide portion 8, the guide portion 8 should be manufactured as a separate large-scaled structure. Also, since the horizontal load generated from the heavy-weight upper structure should be supported, a diameter of the guide portion 8 is increased, and thus the guide portion 8 is necessarily manufactured to have sufficient strength.
In addition, because of the increased weight of the structure and separate production of the structure, a manufacturing cost is increased.
Since the upper plate 9b for supporting the upper structure 2 is supported by the pair of hydraulic units 7a and 7b and the guide portion 8 interposed between the hydraulic units, a little tilting which can be produced by the pair of hydraulic units 7a and 7b and the guide portion 8 cannot be allowed. Therefore, a fatigue loaded is structurally accumulated due to the continuous generation of the horizontal load of the carrier 3 or the upper structure 2.